Update dependabot.yml for dependency version updates

[kanwalpreetd]

What

Updating dependabot.yml to enable dependency version updates for cargo packages through Dependabot. This config sets cargo version updates to run on a weekly schedule, groups PRs for version updates according to major vs minor/patch updates, and sets max PRs that Dependabot can create for version updates per package-ecosystem.

Also, automatic PRs for security updates through Dependabot are already enabled through a global setting. PRs for security updates will be grouped as much as possible across directories and per ecosystem through the global setting (grouping-dependabot-security-updates). But dependabot.yml can also be used for more granular security updates settings in addition to version updates (some of the options in dependabot.yml are shared across security and version updates), such as:

• Grouping security updates according to custom criteria: overriding-the-default-behavior-with-a-configuration-file
• Only allowing automatic PRs for security updates for certain dependencies by configuring allow directive to a certain value such as production, development, direct, indirect. By default, security updates are applied to all dependencies (direct, indirect, production, development).
• Etc.

Why

To enable using the latest cargo package versions, and provide a way to customize Dependabot security updates PRs.

Known limitations

If stability is a concern and regular version updates for cargo packages are not ideal, feel free to close this PR.